1. Field
The presently disclosed subject matter relates to a semiconductor light source apparatus including a phosphor layer for wavelength conversion, and more particularly to a high power semiconductor light source apparatus using a laser light as an excitation light, which can improve a light-emitting efficiency by efficiently combining the laser light into the phosphor layer, and which can also emit various color lights including a natural light having a large amount of light intensity in order to be able to be used for a laser headlight, general lighting, a stage light, a street light, etc.
2. Description of the Related Art
Semiconductor light source apparatuses that emit various color lights including white light by combining a phosphor with a semiconductor light-emitting device such as an LED have been used for business machines, home electronics, etc. Recently, because brightness of the semiconductor light source apparatuses have improved, a range of application for the semiconductor light source apparatuses has expanded to fields such as general lighting, street lighting, vehicle headlights, etc.
In accordance with one method for improving the brightness of the semiconductor light source apparatuses including the phosphor, an excitation intensity of the phosphor can be enhanced by employing a laser light as an excitation light for the phosphor because the laser light has a high light-emitting intensity in general. Therefore, various semiconductor light source apparatuses having a high light-emitting efficiency and a high color rendering index using the laser light as the excitation light have been developed.
A dome-shaped semiconductor light source apparatus using a phosphor layer and a laser light is disclosed in Patent Document No. 1 (Japanese Patent Application Laid Open JP2005-537651). FIG. 16 is a schematic cross-sectional view showing a first conventional semiconductor light source apparatus using a phosphor and a laser light, which is formed in a dome shape and which is disclosed in Patent Document No. 1.
The first conventional semiconductor light source apparatus 90 includes: a sub mount substrate 92; a laser diode 91 emitting a laser light as an excitation light and mounted on the sub mount substrate 92; a reflective board 93 for mounting the sub mount substrate 92 along with the laser diode 91 thereon; a lens 95 formed in a dome shape and located on the reflective board 93 so as to cover the sub mount substrate 92 on which the laser diode 91 is mounted thereon; a phosphor 94 disposed underneath an inner surface of the lens 95 and formed in a uniform thickness; and a transparent resin 96 disposed between the lens 95 and the reflective board 93 so as to encapsulate the laser diode 91 along with the sub mount substrate 92.
Accordingly, the conventional light source apparatus 90 may emit a wavelength converted light by using a laser light emitted from the laser diode 91 to excite the phosphor 94. In this case, although a returning light directed toward the reflective board 93 may occur because a part of the laser light is reflected by the phosphor 94, the returning light may be again returned toward the lens 95 by reflecting the light on the reflective board 93. Hence, the conventional light source apparatus 90 may reduce the amount of light absorbed in the transparent resin 96 and the like, and therefore may improve a light-emitting efficiency.
However, it may be difficult for the conventional apparatus 90 to efficiently use the laser light to excite the phosphor 94 because the laser light may be subject to a back-reflection under the phosphor 94. In addition, it may be difficult for the conventional apparatus 90 to improve a light-emitting density due to a large light-emitting surface, even though the light returning directed toward the reflective board 93 may be repeatedly returned toward the lens 95. Therefore, the semiconductor light-emitting source apparatus disclosed in Patent Document No. 1 may not be a match for a usage such as a vehicle headlight, in which a light source having a high light-emitting density is desired to provide a light distribution pattern that conforms to a standard for a vehicle headlight.
To avoid such a problem, a semiconductor light source apparatus using a light guide in addition to a laser light and a phosphor is disclosed in Patent Document No. 2 (Japanese Patent No. 4,375,270). FIG. 17a is a schematic structural view showing a second conventional semiconductor light source apparatus using a light guide in addition to a laser light and a phosphor, and FIG. 17b is a close up cross-sectional view showing an exemplary light-emitting portion of the semiconductor light source apparatus shown in FIG. 17a, which are disclosed in Patent Document No. 2.
The second conventional semiconductor light source apparatus 80 includes: a laser light source 81 emitting a laser light as an excitation light; a light guide 82 transmitting the laser light; a phosphor 84; and a light-emitting portion 83 connecting the light guide 82 to the phosphor 84 and emitting a wavelength converted light by absorbing and exciting the laser light with the phosphor 84. In this case, because the laser light may be emitted into the phosphor 84 from the light guide 82 formed in a thin circular shape, the semiconductor light source apparatus 80 may enhance a light-emitting density of the wavelength converted light.
However, the laser light emitted from the light guide 82 may also be subject to a back-reflection under the phosphor 84, such that a part of the laser light getting to the phosphor 84 may return toward the light guide 82. Accordingly, a light-emitting efficiency of the semiconductor light source apparatus 80 may not necessarily be high. In addition, because a plurality of light guides 82 may be required to be employed for the above-described usage such as a headlight, a lighting unit using the semiconductor light-emitting source apparatus disclosed in Patent Document No. 1 may become a complex structure in some cases.
To avoid the problem of the back-reflection, a semiconductor light source apparatus using a laser light and a phosphor, in which a reflection ratio of a laser light is reduced on a surface of a light guide including a phosphor, is disclosed in Patent Document No. 3 (Japanese Patent Application Laid Open JP 2009-231368). FIG. 18 is a schematic horizontal cross-sectional view depicting a third semiconductor light source apparatus using a laser light and a phosphor, which is disclosed in Patent Document No. 3.
The third conventional light source apparatus 70 includes: a semiconductor laser chip 71 emitting a laser light as an excitation light; a supporting board 72 including a concave portion 72a with laser chip 71 attached thereto so that a light-emitting surface of the laser chip 71 is exposed to a cavity 73 from the concave portion 72a; and a light guide 74 having an incident surface 74a and a light-emitting surface 74b being inserted in the supporting board 72 and including a phosphor 75 for wavelength-converting the laser light, and wherein the incident surface 74a is configured with a curved surface such that an incident angle of the laser light is within a predetermined range including Brewster's angle.
Thereby, p-wave of the laser light may enter into the light guide 74 without a mirror reflection, and a reflection ratio of the laser light on the incident surface 74a of the light guide 74 may be reduced. Accordingly, the conventional light source apparatus 70 may improve a light-emitting efficiency. However, light entering into the light guide 74 may spread in the light guide 74 due to a light refraction as shown by arrows in FIG. 18, and then may be emitted from the light-emitting surface 74b as a wavelength converted light after it is wavelength-converted by the phosphor 75 dispersed in the light guide 74.
Consequently, the semiconductor light source apparatus 70 may not improve a density of the wavelength converted light because the wavelength converted light emitted from the light source apparatus 70 may be diffused from the light-emitting surface 74b. Thus, the semiconductor light source apparatus disclosed in Patent Document No. 3 may not also be a match for the above-described usage such as for a headlight, in which a light source having a high light-emitting density is desired to provide a light distribution pattern such that conforms to a standard for a vehicle headlight.
The above-referenced Patent Documents are listed below and are hereby incorporated with their English abstracts in their entireties.    1. Patent document No. 1: Japanese Patent Application Laid Open JP2005-537651    2. Patent document No. 2: Japanese Patent No. 4,375,270    3. Patent Document No. 3: Japanese Patent Application Laid Open JP 2009-231368
The disclosed subject matter has been devised to consider the above and other problems, characteristics and features. Thus, exemplary embodiments of the disclosed subject matter can include semiconductor light source apparatuses which can emit a natural light having a high light-emitting efficiency and a high light-emitting density such that can be used as a light source for a vehicle headlight, a projector and the like, and which can improve a light-emitting efficiency by preventing the above-described back-reflection and/or by promoting effective use of the back-reflection.
In addition, exemplary embodiments of the disclosed subject matter can include semiconductor light source apparatuses which can emit various color lights having a high light-emitting efficiency such that the devices can be used as various light sources for general lighting, stage lighting, etc. In this case, the semiconductor light source apparatuses can select a structure for a phosphor layer that converts a laser light used as an excitation light into wavelength converted light having various light distributions, so that the semiconductor light source apparatuses can easily select each of a light-emitting density and a light distribution such as a diffused light, a focused light and the like in accordance with a usage of the semiconductor light source apparatus.